Panic! at the Disks: First Rest-frame Optical Observations of Galaxy Structure at z > 3 with JWST in the SMACS 0723 Field

Abstract

We present early results regarding the morphological and structural properties of galaxies seen with the James Webb Space Telescope (JWST) at z > 3 in the Early Release Observations toward the SMACS 0723 cluster field. Using JWST we investigate, for the first time, the optical morphologies of a significant number of z > 3 galaxies with accurate photometric redshifts in this field to determine the form of galaxy structure in the relatively early universe. We use visual morphologies and Morfometryka measures to perform quantitative morphology measurements, both parametric with light profile fitting (Sérsic indices) and nonparametric (concentration, asymmetry, and smoothness (CAS) values). Using these, we measure the relative fraction of disk, spheroidal, and peculiar galaxies at 3 < z < 8. We discover the surprising result that at z > 1.5 disk galaxies dominate the overall fraction of morphologies, with a factor of ∼10 relative higher number of disk galaxies than seen by the Hubble Space Telescope at these redshifts. Our visual morphological estimates of galaxies align closely with their locations in CAS parameter space and their Sérsic indices.

JWST’s PEARLS: A JWST/NIRCam View of ALMA Sources

“…This would be a surprising result in the pre-JWST era. However, recent JWST/ NIRCam morphological studies of the general galaxy population have shown that disk galaxies are already common at z > 1.5 (Ferreira et al 2022a(Ferreira et al , 2022bJacobs et al 2022). If star formation at z ≈ 1-3 mostly happens in disk galaxies, it can explain why our ALMA source hosts are mostly such systems.…”

JWST PEARLS. Prime Extragalactic Areas for Reionization and Lensing Science: Project Overview and First Results

“…To within the current uncertainties, these conclusions are not unique, but they may point to the need for a more significant fraction of red spiral galaxies at 3.4-4.5 μm, as other recent JWST work has suggested (e.g., Ferreira et al 2022;Fudamoto et al 2022). With the new NIRCam images now at hand, future IGL models may need to include a larger fraction of (dusty) spirals.…”

“…Yet, not all of these galaxies are ellipticals, as discussed below. As the beautiful first NIRCam images already attest, JWST images will thus see a greater dominance of, and emphasis on, earliertype galaxies, which will stand out the most in JWST images (e.g., Ferreira et al 2022). This is in contrast to the "Faint Blue Galaxy" population of actively star-forming galaxies that have dominated HST's UV-optimally images for the past decades (e.g., Driver et al 1995;Abraham et al 1996;Windhorst et al 2011).…”

“…Many caustic-crossing arcs are detected, which are well- of further studies. Relevant for PEARLS, a possible caustic transit candidate has been suggested at z ; 3 in some of the public JWST images of the cluster SMACS0723 (e.g., Chen et al 2022), for which mass models were made by (e.g., Pascale et al 2022), and in which also a significant number of red spirals were identified (e.g., Ferreira et al 2022;Fudamoto et al 2022). Indeed, some very high redshift candidates were already suggested in some of the very first JWST ERS images (Adams et al 2022;Finkelstein et al 2022) et al 1999Venemans et al 2002;Miley et al 2004;Intema et al 2006;Saito et al 2015).…”

“…Ground-based spectroscopic surveys with VLT/ MUSE and the spectrophotometric survey 3D-HST with Hubble suggest that faint galaxies with AB ; 23-29 mag have a median redshift in the range z med ; 1-2 (e.g., Skelton et al 2014;Inami et al 2017) with the caveat that the completeness of these surveys becomes more difficult to quantify at fainter magnitudes. Around this median redshift, the faint end of the galaxy counts samples the power law part of the Schechter luminosity function (LF), which also has a faint-end flux slope α ; − 1.4 to −1.5 at z ; 1.5 (e.g., Hathi et al 2010;Finkelstein 2016). In conclusion, over the AB ; 22-29 magnitude range sampled by our 0.9-4.5 μm NIRCam images, the PEARLS galaxy counts have a slope consistent with the faint-end slope of the Schechter LF at the median redshift sampled by these objects.…”